Status

Current state: [One of "Under Discussion", "Accepted", "Rejected"]

Discussion thread: here [Change the link from the KIP proposal email archive to your own email thread]

JIRA: here [Change the link from KAFKA-1 to your own ticket]

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

Zookeeper brokers currently register 0 for every controller metric. They do this because in the case of a controller failover, the metrics of a newly elected controller will no longer be 0. KRaft does not have this issue because processes with the "broker" role are never elected as the active controller. There is some performance overhead associated with registering metrics, so moving forward it would be best if KRaft brokers do not expose controller metrics.

Public Interfaces

The behavior of which nodes register controller metrics will change for KRaft nodes to only expose the metrics on the controllers.

Proposed Changes

Zookeeper brokers expose 0 for controller metrics. KRaft brokers should not.

Compatibility, Deprecation, and Migration Plan

• Certain tools that expect brokers to expose controller metrics may need to be extended for KRaft to no longer expect brokers to expose controller metrics.

Rejected Alternatives

• Expose 0 on KRaft brokers for controller metrics.
  • There is non-negligible performance impact associated with doing this, so it would be best to change the behavior of controller metrics moving forward instead.